This project is focused on the identification of physiologically critical functions and mechanisms of action of NF-kB transcription factors and their regulators in health and disease. NF-kB is a family of related dimeric transcription factors that serve as primary intracellular mediators during innate and adaptive immune responses. In addition, and importantly, aberrant regulation of NF-kB plays a major role in inflammatory and autoimmune diseases as well as in numerous tumors. It is thus imperative to understand the functions and mechanisms of action of individual NF-kB factors and their regulators, as this will be required to devise appropriate strategies for therapeutic interventions aimed at curtailing aberrantly regulated NF-kB in a precisely targeted manner. To identify physiologic roles and mechanisms we make use of mouse models engineered to lack components of the NF-kB transcription factor family or their regulators, as well as models in which the NF-kB factors can be selectively activated. Our work is focused on so-called alternatively, but also classically activated NF-kB, but especially on the regulators Bcl-3 and IkBzeta. The alternative NF-kB activation pathway is normally initiated by a subset of TNF receptors. Bcl-3 and IkBzeta are atypical IkB family member that function as nuclear regulators of NF-kB activity. We previously discovered a critical role for Bcl-3 in the ability of dendritic cells to properly prime T cells to proliferate in response antigen, and thus to initiate a protective adaptive immune response to pathogens, such as to Toxoplasma gondii, a serious health risk in immune-compromised patients. In the absence of Bcl-3 in dendritic cells, mice succumb to this infection. Bcl-3 also has critical functions epithelial cells, such as in keratinocytes, where it helps to delimit hypersensitivity reactions. Of particular interest is our previous discovery that Bcl-3 is required in T cells to drive T-cell dependent autoimmune diseases, including experimental autoimmune encephalomyelitis, a model for Multiple Sclerosis, and T cell transfer-induced colitis, a model for Inflammatory Bowel Disease. In addition, we recently discovered that in contrast to its pro-tumorigenic role in B cells, it has a tumor-suppressive role in gut epithelial cells. Mice lacking Bcl-3 in these cells exhibited an increased tumor rate in a colitis inflammation-induced colon cancer model, highlighting the context-specific functions of the regulator. In FY2018 we have made considerable progress towards our long-term goal to identify context-dependent functions of Bcl-3, its mechanisms of actions and its transcriptional targets. We have carried out a series of RNAseq experiments in vitro and in vivo and are analyzing and verifying results to understand genes and pathways controlled by Bcl-3 in specific cell types. After a particularly challenging series of experiments we have furthermore succeeded in generating mice in which Bcl-3 carries a small Tag which can be conditionally-attached in a cell-type specific manner. These Bcl-3-tagged mice provide a path - for the first time - to identify chromatin targets of this regulator in mice under various conditions, and specifically in induced, T cell-dependent autoimmune diseases. This tool will additionally allow us to identify proteins via mass spectrometry that interact with Bcl-3 in primary cells.. We have also established the LCMV viral infection model to elucidate the role of Bcl-3 in formation of CD8 T cell memory. This important in part because CD8 T cells that are skewed towards the memory phenotype are most effective in immunotherapy for cancer. We have begun to pursue cell-specific functions and mechanisms of IkBz in the context of psoriasis, making use of a mouse model in which this NF-kB regulator can be conditionally ablated.